I learned or was told years ago that sell price for food or plate was 3X’s cost. For some items it was less and others a little more. This was for fixed stores. So if a dog cost 50 cents (meat, bun, condiments and paper goods)to make, then your competitors will be selling it for $1.50 not $2.50 (50 cents + $2).
Now you also have to look at your break-even point for the day or month. This is the cost of doing business wherether your working or not. Untill you reach this point each day your working for free.